http://www.radio-electronics.com/info/circuits/opamp_notch_filter/opamp_notch_filter.php 
, or similar ones elsewhere.

Bruno L. Albrecht wrote:
> Hi,
> I'm trying to separate 3 frequency components from an analog signal. The
> original signal is composed by the sum of 3 frequencies (1500, 4000 and
> 10200 Hz) and some noise. The objective is to separate only those 3
> frequencies and evaluate their magnitudes. I thought about lots of ways of
> doing it, but couldn't get an effective one.
> Any ideas?
>
> Cheers,
>  Bruno
>   

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